1. Field of the Invention
This invention relates to a powerful fiber laser system and, in particular, to an optical coupler configured to monitor the power of forward and backreflected light signals propagating along a light path in forward and backward directions, respectively.
2. Prior Art Discussion
A powerful fiber laser system typically includes one or more laser cascades and is capable of outputting tens and hundreds of watts. A light signal propagating along a powerful fiber laser system may vary within a broad range. The instability of the propagating signal detrimentally affects the task to be performed by a powerful laser system and the functionality of the system's components. To monitor the variation of power of light signals, optical laser systems are provided with taps. The purpose of such taps is to bleed off a small portion of optical signal so as to analyze the signal for desirable characteristics by a photo-detector.
Quite often, to prevent detrimental effect of light backreflection that may be caused by inner obstacles, such as splices coupling adjacent fibers, optical isolators are coupled between the cascades. The backreflection can be also caused by an outer obstacle, such as the surface to be processed during, for example, cutting and welding processes. Typically, a hybrid structure configured with an isolator and tap is installed in a powerful laser system
The taps alone or in combination with isolators come in a variety of configurations. FIGS. 1 and 2, for example, illustrate a multi-cascaded fiber laser system 10 including an input cascade Li 11 and at least one output cascade Lo 12. A power monitor 14 preferably, but not necessarily, is coupled to the output of output cascade 12 and includes serially coupled an isolator core and a fiber tap. The fiber tap is configured with a fiber tap source and a photo detector 16, as illustrated in FIG. 2. Typically, detector 16 is located adjacent to a fiber bent or a taper where leaking light of the propagating signal may be sensed by detector 16. Based on multiple measurements, the stability of such a tap, i.e., the ratio between the measured power and the actual power of the propagating signal, is high and may reach about 10%. As a result, the measurement data of the actual power may be imprecise and lead to unsatisfactory performance of the laser system.
A need, therefore, exits for a power monitor operative to provide improved measurements of the power of light signals generated by a powerful laser system.
A further need exists for a photo detector configured to withstand relatively high powers of the tapped signal.